Connections between arrays of optical fibers and arrays of other optical conveyances including active and passive devices such as emitters, receivers, MEMS (MicroElectroMechanical Systems), and planar waveguides enable the distribution of optical information throughout networks, particularly optical communications systems. Optical fibers supported in array formats can also be used to gather or distribute localized light for other purposes including illumination and optical data acquisition.
Optical networks incorporate various combinations of emitters, receivers, routers, MEMS, and other active and passive components, all requiring connections to bundles or other groups of optical fibers. Couplings between the optical fibers and other such optical conveyances are often made individually. To minimize losses of light, the couplings generally require exact alignment between the optical fibers and the other optical conveyances. Entrance and exit apertures must also match, or focusing optics can be required to resize or reshape the light into a corresponding form. Once aligned, the individual fibers and optical conveyances must be secured together.
Connections between individual optical fibers and other optical conveyances are exacting and costly. Efforts to simplify and expedite the coupling of groups of fibers have included the use of coupling mechanisms, such as V-grooved blocks, for spacing, aligning, and securing rows of fibers to corresponding rows of other optical conveyances including other rows of optical fibers. Although coupling by row is more efficient than coupling fibers individually, the coupling of large numbers of rows of fibers can still be costly and time consuming.
More efficient couplings have been made between two dimensional arrays of optical fibers and corresponding arrays of active components including lasers and other opto-electronic emitters or receivers. One example allows for the mounting of individual fibers within openings in a key structure containing optical waveguides. The key structure mates with a keyway machined into a another structure containing corresponding waveguides in communication with a plurality of semiconductor chips. The fibers must be carefully mounted in the key structure to avoid losses, and the additional interface between the key and keyway structures further reduces efficiency.
Another opto-electronic circuit package features a lid containing an array of laser-drilled holes for receiving a two-dimensional array of fibers. The lid containing the fiber array is mounted on a base in alignment with a circuit die containing an array of emitters or receivers. Both the circuit die and the lid are referenced with respect to the base to align the fiber array with the array of emitters or receivers. The individual formation of closely spaced holes in the lid is difficult to accomplish with the required consistency and precision.
My invention utilizes preforms, particularly glass, glass-ceramic, or ceramic preforms in the shape of cylinders or other solid forms, for arranging an array of optical fibers in a predetermined configuration. The preform, which has formed within it a pattern of holes for supporting the optical fibers, is adjusted in size for positioning the fibers in a predetermined pattern. So arranged, the fibers can be collectively aligned and coupled to similarly pattered arrays of other optical conveyances, including arrays of emitters, receivers, and various waveguide structures. Improved efficiencies, lower cost, and ease of manufacture are anticipated as benefits.
One example in which my invention can be used to arrange optical fibers in a desired array format begins with an original preform having an axis and axially extending holes arranged in a predetermined pattern. Both the size of the holes and their spacing are preferably oversized with respect to the intended pattern for arranging the fibers. Heat is applied to the preform, if necessary, to transform the preform into a malleable state; and a cross-sectional reducing force is applied to reduce the scale of the predetermined pattern of holes in the preform. A transverse section of the preform containing a desired reduction in the scale of the hole pattern is removed. Optical fibers are mounted in the holes to arrange the fibers in the desired array format.
Fabricating the original preform can be accomplished by various means including extruding a blank through a die that forms the axially extending holes or assembling the preform from a bundle of rods or tubes. The preform itself is preferably made of glass, glass-ceramic, or ceramic to provide thermal stability to the final array. The cross-sectional reducing force can involve the application of various pushing and pulling forces including combinations of such forces. For example, a drawing force can be applied that stretches the preform along its axis to reduce a scale of the predetermined pattern of holes as a function of drawn position along the axis of the preform. The transverse section removed from the preform is taken from a position along the preform axis at which the predetermined pattern is reduced to the desired scale. Alternatively, an extruding force can be applied along the preform axis to push the preform through a conventional reducing die for similarly reducing the scale of the predetermined pattern of holes along the axis of the preform.
Preferably, the preform is cylindrical in shape having an initial diameter at least 25 percent larger than the diameter of the transverse section removed from the reduced preform. The fibers can be mounted in the preform either before or after the preform is reduced in size. For example, the fibers can be mounted and secured in the holes of the transverse section after it has been removed from the preform, or the fibers can be mounted in the preform before it is reduced and can be secured in the holes by their subsequent reduction in diameter. To protect the fibers during the reduction, the preform can be made of a material with a lower transition temperature than the material content of the fibers.
My invention can also be practiced as a way of coupling an array of optical fibers to an array of optical conveyances. The preform is fabricated having an array of axially extending holes. Collapsing the preform about its axis reduces a spacing pattern of the holes. A transverse section removed from the collapsed preform contains a spacing pattern of the holes matching a spacing pattern of the optical conveyances within the array of optical conveyances. The optical fibers are assembled within the holes into the array of optical fibers, and the transverse section of the collapsed preform is mounted along with the assembled fibers together with a common support of the array of optical conveyances for collectively aligning the array of fibers to the array of optical conveyances.
Tips of the fibers can be preshaped prior to insertion into the preform or can be collectively treated after insertion to provide apertures compatible with those of the individual optical conveyances. For example, a mating surface of the transverse section of the collapsed preform can be polished together with protruding tips of the fibers to provide a consistent mounting surface adjacent to the array of optical conveyances. If reshaping of the light entering or exiting the optical fibers is required, a lens array can be inserted between the transverse preform section and the common support of the optical conveyances to improve coupling efficiency between the array of fibers and the array of optical conveyances.
The optical conveyances ordered within the array can include active or passive optical components including lasers, MEMS, and other devices for performing various functions. For example, a two-dimensional array of optical conveyances can be formed by a stack of optoelectronic or optoelectromechanic devices. The common support for the optical conveyances can also be a single wafer having optoelectronic (or optoelectromechanic) features formed in its surface such as vertical cavity surface emitting lasers (VCSELs). Active or passive waveguide structures can also be used in either a stack or surface communicating form. The transverse section of the preform, the lens array, and the common support for the optical conveyances can all take plate-shaped forms that can be readily stacked together to form an efficient compact coupling structure.
Preferably, both the array of fibers and the array of optical conveyances are arranged as two-dimensional arrays. Alignment of the arrays can take place by aligning two relatively displaced fibers with two corresponding optical conveyances or by matching features of the sectioned preform with corresponding features on the common support for the optical conveyances. Combinations and variations of these techniques are also possible for collectively aligning the array of optical fibers with the array of other optical conveyances.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention and are intended to provide an overview or framework for understanding the nature and character of the invention as claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of the specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention.